Oil extended gr-s rubber having unusual low temperature retraction characteristics



United States Pfltfllt No Drawing. Application sep temb'er'z, 1953 Serial No. 378,168

claims." (21. 260 -335 This invention relates to rubber compositions.- A more specific aspect of this invention r'elates'to' rnbnereom ositions having improved characteristics obtained by employing novel processing oils in the preparation of the rubber compositions. in a still more specific aspect, the present invention relates to the utilization of refined mineral oils as processing oils in the preparation of synthetic rubbers.

2,900,357 'Pate'nted' Aug. 18; 1959 devised. Heat-softening is oiie method which has" been used for reducing the Mooney viscosity of artificial rubber (particularly hot rubber). However, this methoil has not been too successful from a commercial standpoint. From the standpoint of processing ease, it was determined that the addition or oils, such as those pre- Prior to the introduction of synthetic rubbers during World War II, vegetable and mineral oils and materials of like character hadbeen used small amounts iri'the processing of natural rubbers. In this particular application, a small 'amountof the oil was added to the rubber in its latex fornras a softening agent to reduce power consumed in mixing and mastication of the rubber mass. Likewise, small amounts of vegetable and mineral: oils had also been used inreclaimingrubbers and, thus, were incorporated in finished products which often contained vi'ou'sly employed as softeners oi plasticizers, reduced the Mooney viscosity to the extent desired and had no detrimental effect on the physical properties of the product. It was also found that these processing oils could be used in amounts far in excess of the amounts normally used in softening and plasticiz'iiig to replace a certain amount of the synthetic polymer and thus extend the polymer. The use of oils of petroleum origin as extenders or processing oils for natural rubber and synthetic elastoniers was first proposed in 1936. The first product in: troduced for this purpose was Naftolen, a petroleumoil recovered from the acid sludge produced in the treat nient of petroleum oils with sulfuric acid. This material was used commercially as a rubber extender just lief fore and during World" War II; Early Work with Naftolen indicated that the carbon black content of the rubbershouldbe increased with the increase in'the proportion of Naftolen used in the rubber. In its capacity as an extender, Naftolen was shown to be suitable for v 7 use innatural rubber, GR-S, and reclaimed rubber. In

a substantial amountof reclaimed rubber as a' component. a

v The short supply of'rubber and the introduction of synthetic rubbers during World War II brought a number of new problems to the rubber industry and neces= sitated much work before the synthetic rubbers could be used successfully. Many of these problems involved modi fiers and extenders for the new rubbers and for formula tions involving admixtures of the new rubbers with fiatural rubbfer.

The most important synthetic rubber developed was ther and more recent discovery was that polymers pro duced by more complete polymerization'of' the same mix ture of butadiene and styrene were superior. in' quality to either the hot or cold rubbers formerly produced: These high-molecular weight: products are polymerized toa degree suchthat .their Mooney viscositi'es are substantially above 65 when measured at 212 F. for-4 minutes. example of-such-products is Po1ygenGR=S' produced by General Tire; and Rubber Company.

; Since syntheticrubber lias zahigher Mooney viscosity" than natural rubber and the ofr'ubber is depeud view of the developments outlined above and the, successful use of Naftolen, anumber of petroleum oil extenders so'on appeared on the niarket. Naphthenic oils, such as Circosol 2XH, as well as highly aromatic oils, Such as extracts from the solvent extraction of lubricating oils, were used commercially. Although praea'cauy; any aromatic or naphthenic mineral oil can be employed with fair results when relatively small amounts of oil (in the neighborhood of about 25 parts of oil per parts of rubber polymer) are incorporated, synthetic elastorners are more sensitive to. the type of oil when larger amounts of oil are employed. This is particularly true in the case or high Mooney viscosity GR-S rubbers, which tolerate amounts of oil as high as 100 parts of oil per 100 parts of rubber polymer. While rubbers prepared with large amounts of aromatic or naphthenic petroleum oils are satisfactory in most respects, these rubbers are notably inferior so far as their low temperature retraction properties arerconcerned. This failure of rubbers containing largeamounts of commercially known processing oils to" regain their original shape at a suitable rate at low tem' peratures is particularly vexing when the rubbers'areused in. the preparation of pneumatic tire tread stocks:

It is, therefore, an object of the present invention to provide an improved rubber composition;

It is another and further object .of the'present' invention toprovide a rubber composition having improved lowtemperature retraction characteristics; r

A further object of this invention is to provide an improved pneumatic tir'e' stock having improved 15w te in peratu're'retraction characteristics.

Still another object of this invention istoprovide a rubber composition extendedwith large amounts of' improved processing oil.

Another and further object of this invention is to provide a high Mooney viscosity GR-S rubber having improved low temperature retraction characteristics.

A still further object of this invention is to provide an improved high Mooney viscosity GR-S rubber containing large amounts of a novel processing oil.

Another object of this invention is to provide an improved high Mooney viscosity GR-S rubber tire stock containing a novel processing oil.

Other and further objects of this invention will be apparent from the following detailed description of this invention. I V a Contrary to the teachings of the prior art, it has been found that highly paraffinic mineral oils may be used as'rubber extenders in the processing of synthetic and natural rubbers. In a more specific aspect, it has been found that a solvent refined paraffinic petroleum oil boiling in the lubricating oil range is far superior to commercially available aromatic and naphthenic rubber processing oils, particularly in the low temperature retraction propertieswhich it imparts to high Mooney vis cosity GR-S rubbers. V

In order to demonstrate the advantages of the processing oils of the present invention, a number of rubbers were prepared using the following formula:

Parts High Mooney viscosity GR-S polymer 100.0 Petroleum oil 50.0 Philblack O 75.0 Zinc oxide 3.0 Stabilite 0.8 BLE 0.8 D.P.G. 0.2 Santocure 1.1 Sulfur 2.1

The high Mooney viscosity GR-S polymer was produced by the co-polymerization of approximately 28 parts of styrene and 72 parts of butadiene at approximately 41 F. The ingredients shown above were milled using as the petroleum oil a solvent refined neutral oil havin the following characteristics:

Table I below, wherein the paraflinic oil described is referredto as Paraflinic Oil 1:

Table I Extender used. Paraflinic Circosol Oil 1 2XH 300% Modulus (45 min. cure at 287 F.) 1, 775 1. 400 Tensile (45 min. cure at 287 F.) 2, 675 2, 600 Elongation (45 min. cure at 287 F.) 400 450 Tear (45 min. cure at 287 F.)- 178 199 Hardness (45 min. cure at 287 F.) 56 55 Rebound (60 min. cure at 287 F.) 61.5 53.9 Mooney Plasticity:

ML 1.5 min. at 212 F 56 43 ML 4.0 min. at.2l2 F 50 I 39 'Ifgsltls e n rubber aged 48 hours in oven at Tensile (45 min. cure at 287 F.) 2, 150 2,000 Elongation (45 min. cure at 287 F.) 230 270 Hardness (45 min. cure at 287 F.) 66 65 Tensile Retraetion on Cured Rubber:

1% Recovery O -65 48 2% C .61 46 60 45 -56 -13 53 41 50 -37 -48 36 -46 43 -31 28 36 24 a2 -19 w 25 -12 It will be seen from the results shown above that the rubber containing the preferred processing oil of this inavailable processing oil.

vention is similar to that containing the Circosol 2XH with the exception of tensile retraction. With regard to this particular property, it is obvious that the rubber extended with the processing oil of this invention is vastly superior to that extended with the commercially Further, tests have shown that aromatic extenders are the same as or are inferior to Circosol ZXH with respect to their ability to impart good low temperature retraction properties to GR-S. The rubbers prepared with the preferred extender of this invention are particularly useful in the preparation of pneumatic tire tread stocks. Flat spots in the tire tread formed .as a result of low temperature parking of vehicles will disappear more rapidly if the tire is composed of rubber extended with processing oils of this invention.

Road tests of tires prepared from GR-S rubbers extended with the processing oils of this invention have been made. These tests show that the improved rubbers of the present invention are superior in wear characteristics to those prepared in accordance with prior art 7 methods.

The processing oils of the present invention may be added to the rubbers by (l) emulsification with water and coprecipitation of the mixture of oil and rubber emul sions (masterbatching), (2) direct milling into precipi- I SUS are unsatisfactory for use in the preparation of synthetic rubbers. Attempts to incorporate a solvent refined Gravity API) 31.5 Flash (C.O.C.) F.) Fire (C.O.C.) F.) 470 Vie/ F. (SUS) 166.1 Vis./210 F. (SUS) 44.6 Viscosity index Pour (max) 5 Color (NPA) +1 Aniline point F.) 219.9 Acid No. (ASTM method D974-51T) 0.03 Ash (oxide) (percent) 0.01 1 Carbon residue (Conradson) (percent) 0.00 Sulfur (percent) 0.21 Bromine No 1.4

Refractive index (n 1.4780 Evaporation test (280 F):

Loss in 6 hrs. (percent) 3.37

Loss in 12 hrs. (percent) 5.70 Rostler analysis:

Nitrogen Bases (percent) i 0.4

1st Acidifins (percent) 0.0

. 12nd 'Acidifins (percent) 20.4 Saturates (percent) 79.2

oil having 'a-viscosity of 151.7 SUS at 210 F. were unisuccess'ful due to the fact that the'oil was incompatible with the rubberfpoly'mers. Therefore, the preferred oils of the present invention are oils having a viscosity of approximately 30 to SUS at 210 F. Table II below oil Circosol ZXH, a commercially available naphthenic outlines the characteristics of several processing oils Table H i .Paraflinie: zi arafiinio Dill a i12 Gravity API) v 31.5, 30.0 Flash (0.0.0.) F.)--. 420" "465 FireKGr-O-O $701 525 Via/100 so 166,1 41o Visa/210 BUS)- 44:6 5914i Viscosity Index---- -105 Pour (Max.) 5 0 Color (NPA) +1 2+ Aniline Point (,F.),.. 219. 9, 237. 2 Acid N o. (AS-TM Method D9 0:03 0.07 Ash (Oxide) (Percent) 0.01 Nil CgbQlDRESidlle (Conrad at) 41100: 07 S fur (Pereeiit) 0.21 I 0.26 Bromine No 1'54 15.5 Refractive Index .(nD20iC.-)..-;-- v, 1.;4820 Evaporation Test (280 -F.)'

Loss in 6 hrs. (Percent)... 1:40

Loss in 12 -hrs.('Percent) ,2. 17 Rostler Analysis? Nitrogen Bases (Percenth 1st Acidifinsi-Percent); "2nd itcidifins' (P re'eiitl saturates (Percent) In the preparation of rubber products containing the parafiinic oil extenders of the present invention, amounts of oil extender up to 100 parts of extender per 100 parts a to 50 parts of oil per 100 parts of rubber hydrocarbon 3e preferred.

'7 in addition to the extender, the rubber composition 'n rnally contains other additives, of which one is necessarily the vulcanizing agent. Suitable agents of this character are sulfur, sulfur chloride, certain thiocyanates, thiuram polysulfides, and other organic and inorganic polysulfides, organic and inorganic peroxides, halogencontaining compounds and nitrogen-containing compounds such as the nitrobenzenes.

Vulcanization accelerators and accelerator-activators may also be present. Illustrative examples of accelerators are N-cyclohexyl-Z-benzothiazole sulfenamide (Santocure), diphenylguanidine, mercaptobenzothiazole and its derivatives, thiuram disulfides, thiuram monosulfides and dithiocarbamates. The metal oxides, such as zinc oxide and lead oxide are ordinarily added as acceleratoractivators. It is also common practice to add a fatty acid such as stearic acid or oleic acid as an accelerator-activator in addition to the metal oxide.

Age deterioration of rubber goods is generally reduced by the addition of antioxidants such as phenyl-beta-naphthylamine, amine reaction products known in the trade as BLE, and Agcrite products such as hydroquinone mono benzyl ether, aldol-alpha-naphthylamine, di-betanaphthylpara-phenylenediamine, and diphenyl-ethylene diamine (Stabilitc).

' Carbon blacks such as Philblack 0, high abrasion furnace (HAF) blacks, etc., are also major components. These materials act as bodying agents or fillers, thereby improving the tensile strength, tear resistance, and other like properties of the rubber product.

The processing oils of the present invention may also be used in the preparation of a variety of rubbers and rubber products in addition to high Mooney viscosity GR-S rubbers. It is generally conceded that processing oils suitable for use in high Mooney viscosity GR-S rubbers are suitable for use in ordinary GR-S rubbers due to the more stringent requirements of the high Mooney viscosity rubber. It has also been found that the processing oils or" the present invention may be used in the preparation of rubbers from co-polymers of olefins and diolefins, such as Butyl rubbers normally used in the preparation of vehicle inner tubes. Likewise, processing oils of this invention may be used in the preparation of a Wide variety of specialized rubbers, such as the light-colored rubbers used in preparing white side-wall tires and like rubber articles. Processing oils of the present invention may also be used for other purposes, such as of rubber hydrocarbon may be employed. However, 25

SUS at 10f E, and being presentin compos an arno :sufiicient'to improve sfu 1y the'lo nipera'ture'. retraction characterstics of the rubber upon vulcanization, of thefcomposifion, v r

'compo'sitionlacc' 11g to claim 1 in whic h said ,S'Yflthbt 1 15b? is. bil'failii y l fi 3'. An improved ble rubber composition ris ng, a i l b y 1 1 s -po y v n a 'Mo'oney viscosity "substantially above 65 at 212 F. for four minutes, having permanently incorporated therein a rubber extending amount of a mineral oil consisting of the phenol-free rafiinate phase obtained in the phenol extraction of a petroleum fraction boiling in the lubricating oil boiling range and obtained from a parafiinic base crude, said mineral oil consisting essentially of a predominant proportion of saturates and a minor proportion of second acidifins by Rostler analysis, having an average viscosity of 30-150 SUS at 210 F. and being present in said composition in an amount suflicient to improve substantially the low temperature retraction characteristics of the rubber produced upon vulcanization of the composition.

4. The composition according to claim 3 in which said mineral oil is present in the amount of 25-100 parts by volume per parts of said polymer.

5. A pneumatic tire stock having improved low temperature retraction characteristics comprising, a rubbery butadiene-styrene co-polymer having a Mooney viscosity substantially above 65 at 212 F. for four minutes, having permanently incorporated therein 25 to 50 parts per volume per 100 parts of said polymer of a mineral oil consisting of the phenol-free raifinate phase obtained in the phenol extraction of a petroleum fraction boiling in the lubricating oil boiling range and obtained from a paraffinic base crude, said mineral oil consisting essentially of a predominant proportion of saturates and a minor proportion of second acidifins by Rostler analysis and having a viscosity of about 30-150 SUS at 210 F.

6. The pneumatic tire stock according to claim 5 in which said mineral oil is composed of about 79% saturates and 20% second acidifins.

7. A pneumatic tire stock having improved low temperature retraction characteristics comprising, a rubbery butadiene-styrene co-polymer having a Mooney viscosity substantially above 65 at 212 F. for four minutes, having permanently incorporated therein 25 to 50 parts per volume per 100 parts of said polymer of a mineral oil consisting of the phenol-free raflinate phase obtained in the phenol extraction of a petroleum fraction boiling in the lubricating oil boiling range and obtained from a paraffinic base crude, said mineral oil consisting essentially of a predominant proportion of saturates and a minor proportion of second acidifins by Rostler analysis and having a viscosity of about 30-150 SUS at 210 F., a vulcanizating agent, a vulcanization accelerator, an accelerator-acti- V vator,.an anti-oxidant, and a bodying agent softeners*forithe reclaiming ofnatural andsynthet'ic rut me per 100 parts-of said polymer of a mineral oil consistingof the phenol-free raflinate phase obtained in' the phenol extraction of a petroleum fraction boilingfin the lubricating oil boiling range and ,obtained from a paraffinic' base crude, said mineraloil consisting essentially. of a predominant proportion of saturatesyand a minor proportionof second acidifins by Rostler analysis and having a viscositygofiabout 30-150 SUS at 210 F., a carbon black, (sulfur, diphenylguanidine, N-cyclohexylQ-benzm thiazol'e sulfenamidqan'antioxidant organic amine, and ametal oxide. f i i a Y 9. Al pneumatic tire stock having improved, low temperature retraction characteristics comprising, a rubbery butadiene-Vstyr'ene,co polymer having a Mooney viscosity substantially above 6'5'at 212 F. for fourmmuteshaving permanently incorporated therein to parts'per volume per partsof said polymer iof'aniineral oil consisting of the phenol-free rafliinate'jphase' obtained in References Cited in the file of this patent 'RostlerrRubber Age,'volume 69, No. 5, August 1951 .pa'ges 559-577. 1 i Rostler et al.: Ind. and Eng. Chem., volume 41, No. 3

' March 1949, pages 598-608.

Harrington et al.:' 'India Rubber World, volume 124, No. 5,,August 1951, pages 5711-575, V 1

Weinstock et al.: Rubber Age, December 1951, pages Weinstock et a1.: Ind. and Eng. Chem, volume 45, No. 5, May 1953, pages 1035-1943, 

1. AN IMPROVED VULCANIZABLE RUBBER COMPOSITION COMPRISING A SYNTHETIC HYDROCARBON POLYMER RUBBER HAVING PERMANETLY INCORPORATED THEREIN A RUBBER EXTENDING AMOUNT OF A MINERAL OIL CONSISTING OF THE RAFFINATE PHASE OBTAINED IN THE SOLVENT EXTRACTION OF A PETROLEUM FRACTION BOILING IN THE LUBRICATING OIL BOILING RANGE AND OBTAINED FROM A PARAFFINIC BASE CRUDE, SAID MINERAL OIL CONSISTING ESSENTIALLY OF A PREDOMINAT PROPORTION OF ASTURATES AND A MINOR PROPORTION OF SECOND ACIDIFINS BY ROSTLER ANALYSIS HAVING AN AVERAGE VISCOSITY OF 30-150 SUS AT 210* F., AND BEING PRESENT IN SAID COMPOSITION IN AN AMOUNT SUFFICIENT TO IMPROVE SUBSTANTIALLY THE LOW TEMPERATURE RETRACTION CHARACTERISTICS OF THE RUBBER PRODUCED UPON VULCANIZATION OF THE COMPOSITION. 